Table for feeding a plastic film for a bundling machine

ABSTRACT

The invention relates to an feeding table, comprising a pair of rollers ( 13, 14 ), referred to as pressers, arranged downstream from the cutting system, said pair including a motor-driven roller ( 13 ) and at least two driven rollers ( 14 ) which are arranged so as to form at least two pressure tracks engaging with the plastic film ( 6 ) moving between said pair of rollers ( 13, 14 ). Each pressure track includes a driven roller ( 14 ), the shaft ( 23 ) of which is supported by a mobile frame ( 19 ) that is guided on a beam ( 20 ), wherein said beam ( 20 ) is secured to the general frame ( 2 ) and a foolproof system for applying pressure is provided between said beam ( 20 ) and said frame ( 19 ) in order to restrain said driven roller ( 14 ) and hold the latter in tangential contact with the motor-driven roller ( 13 ).

The invention relates to an improvement made to machines for packaging products in plastic film, and particularly to machines known as “bundling machines”.

This type of machine, as described in document FR 2 823 190, allows wrapping groups of products in a length of film of appropriate shrinkwrap plastic.

To guide the end of the plastic film to the products, the bundling machine includes a feeding table which comprises two spaced-apart pairs of rollers: one upstream pair of rollers and one downstream pair of rollers, with a system between them for cutting the plastic film into the desired length. The upstream pair of rollers constitutes the feeding pair, with at least one motorized roller, and the downstream pair of rollers constitutes the tensioning pair, again with a motorized roller.

The tensioning pair is arranged downstream from the system for cutting the plastic film; it is placed in proximity to the passageway existing between the conveyor that feeds the products to be packaged and the conveyor belt of the bundling module where said products are wrapped in the length of film.

The operation of cutting the plastic film occurs between the two pairs of rollers of the feeding table.

To obtain a neat, clean cut of the plastic film, the film is held taut between the feeding pair and the tensioning pair, and this tautness is maintained by adjusting the respective speeds of the pairs of rollers.

Prior to the cutting operation and during the cutting operation, the rollers of the tensioning pair are driven at a speed which is substantially greater than that of the rollers of the feeding pair.

Managing this tension in the plastic film does not depend solely on the difference in the speeds of the pairs of rollers arranged on each side of the cutting system, but also depends on the contact between the film and the various rollers.

Uniform compression across the entire width of the plastic film between the rollers of each pair is difficult to obtain, and in addition, the adhesion is not the same for each pair of rollers.

This adhesion is good for the rollers of the feeding pair which have a relatively large diameter and which are each covered with a rubber material; such is not the case for the rollers of the tensioning pair, because although one of the rollers, the motorized roller, has a large diameter and is covered with rubber, the other roller has a relatively small diameter for reasons of space limitations and, in particular, it does not have a particularly adhesive covering because it is made of steel for rigidity and in order to be wear- and abrasion-resistant.

In the portion of plastic film located between the pairs of rollers, one can observe deformations directly related to variations in the tension of the plastic film, across its width, between the rollers of the tensioning pair and those of the feeding pair.

These tension variations in this portion of film are a source of incidents during cutting operations.

Such tension variations have multiple causes and it is difficult to remedy them by a simple adjustment of the pressure between the rollers of the tensioning pair.

In fact, the use of different types of plastic films may occur, depending on the products to be processed, particularly plastic films of a thickness adapted to the products to be wrapped.

Also, significant thickness variations may be observed within the same plastic film, sometimes reaching values on the order of 30% of the nominal thickness.

In addition, depending on the type of machine, there may be two or three plastic films being fed simultaneously on the belt of the bundling module, in order to package several groups of products arranged in parallel to one other.

The invention proposes an arrangement in this feeding table, and in particular in the tensioning pair, in order to obtain in a simple and permanent manner a uniformity in the contact pressure between the rollers and in particular across the entire width of said rollers, meaning across the entire width of the plastic film, regardless of whether one or multiple plastic films

The feeding table of the invention comprises, along the path traveled by a plastic film, upstream from a bundling module, pairs of rollers for advancing and maintaining tension on said plastic film and a system for cutting said plastic film, said pairs of rollers being supported by a general table frame and being arranged respectively upstream and downstream of this cutting system, and is characterized by one of said pairs of rollers, the tensioning pair, arranged downstream from said cutting system, comprising a pressure roller which is motorized and, associated with this motorized pressure roller, at least two driven pressure rollers, said driven pressure rollers being arranged so as to form at least two pressure tracks pressing on said plastic film which is traveling between said motorized pressure roller and said driven pressure rollers, and wherein each driven pressure roller is made of steel with an axle supported by a roller frame, said roller frame being mobile, guided on a beam which acts as a reference and which is solidly attached to the frame of the feeding table.

Still according to the invention, a foolproof pressure application system is placed between the beam and each roller frame to restrain each of the driven pressure rollers and hold them in tangential contact with the motorized pressure roller.

In a preferred embodiment of the invention, the pressure application system consists of at least one coil spring arranged on the reference beam, said spring being associated with a tappet which is guided relative to said beam, said tappet being in contact with and pressing continuously against the roller frame of the driven pressure roller, due to the force exerted by said spring, the number of tappets and/or springs being chosen to establish an appropriate pressure at said tensioning pair, comprising at least three pressure rollers.

Still according to the invention, each pressure element consisting of a spring and a tappet is arranged in a bore-hole created within the thickness of the beam, said bore-hole comprising, at its end on the roller frame side, a shoulder which serves as a support for a base of said tappet, and at its other end, a plate acting to cover the hole and serving to support said spring, said plate being removable to allow accessing the pressure element, meaning the spring and the tappet, in order to be able to modify the amount of pressure between the pressure rollers and change them if necessary.

In another arrangement of the invention, the reference beam comprises, at its ends, attachment means for fastening it to the general frame of the feeding table, and in particular to a part of this frame which can be retracted to provide access to the pairs of rollers and to the cutting system.

In a preferred arrangement of the invention, the assembly consisting of the driven pressure rollers, their roller frames, and the reference beam, is in the form of a module, said module of driven pressure rollers being equipped with removable attachment means such as screws, to enable its practical and convenient assembly onto the general frame of the feeding table.

The invention is described in a sufficiently clear and complete manner in the following description to enable its execution, accompanied by drawings in which:

FIG. 1 represents a schematic elevated view of the feeding table installed on a machine for packaging a group or batch of objects;

FIG. 2 is a schematic view showing a module of driven pressure rollers;

FIG. 3 shows the details of the system for applying pressure on a driven pressure roller.

FIG. 1 shows a schematic view of a feeding table 1 of the type found in bundling machines.

This bundling machine comprises, assembled onto the same general frame 2, a conveyor 3 which feeds the products and groups of products 4 into what corresponds to the actual bundling module 5.

The plastic film 6 from which lengths are to be cut comes from a spool 7 which is installed on a unwinding stand 8 supported by the frame 2 of the machine. This plastic film is introduced between the conveyor 3 and the belt 9 of the bundling module 5, through the passageway 10.

The plastic film 6 traverses the feeding table 1 which comprises two pairs of rollers, and a system for cutting said plastic film 6 is located between these two pairs of rollers.

The feeding table 1 therefore comprises:

-   -   a first pair of rollers 11 and 12, called the feeding pair;     -   a second pair of rollers 13 and 14, called the tensioning pair;     -   a cutting system which comprises a rotating knife 15 and a fixed         counter-cutter 16.

The feeding pair consisting of the rollers 11 and 12 is arranged upstream from the cutting system and the tensioning pair consisting of the rollers 13 and 14 is arranged downstream from said cutting system.

Each pair of rollers comprises a motorized roller; thus, as represented in FIG. 1, the roller 11 and the roller 13 are motorized and the corresponding rollers 12 and 14 are simply driven. The motorized rollers 11 and 13 are, preferably, arranged on the fixed part 2 a of the general frame 2; the driven rollers 12 and 14 are arranged on the frame 2 as well, but preferably on a portion 2 b of this frame 2 which allows opening the feeding table and accessing the space between the rollers of each pair of rollers.

The plastic film 6 passes between these two pairs of rollers 11 to 14 and also passes between guides 17, said guides 17 being fixed, solidly attached to the frame 2, and being respectively associated with each of these various rollers 11 to 14.

The plastic film 6 also traverses the cutting system; it passes between the knife 15 and the counter-cutter 16, which are arranged so that when in the inactive cutting position they together form guiding means for said plastic film 6.

To perform the cutting operation, the control means for the motorized rollers 11 and 13 arrange a slight difference in speed between these two rollers 11 and 13, which has the effect of creating tension in the portion of plastic film 6 located between this upstream roller 11 and this downstream roller 13.

To obtain a cut that is neat and clean, the plastic film 6 must be uniformly taut across its entire width.

A uniform contact pressure between the plastic film 6 and the pressure rollers 13 and 14, across the entire width of the film 6, is obtained by an arrangement of several pressure tracks along the width of said rollers, with at least two such pressure tracks.

These pressure tracks correspond to the area where multiple driven pressure rollers 14 press against the motorized pressure roller 13.

As represented in FIG. 2, two driven pressure rollers 14 are mounted, independently of each other, each in a roller frame 19, said frame 19 being supported by a beam 20 which acts as a reference beam relative to the frame 2 of the machine and this beam 20 is solidly attached to the general frame 2 of the machine by means which will be detailed below.

Each roller frame 19 comprises flanges 21 and 22 at its ends, which receive the axle 23 of the roller 14; this frame 19 is mobile relative to the beam 20 and is appropriately guided by rail systems 24.

The rail systems 24 define the travel d of the roller frame 19 relative to the beam 20. This travel d between the frame 19 and the beam 20 is on the order of 2 mm for example.

Note the presence of several elastic means 25 between each roller frame 19 and the beam 20. These elastic means 25 are represented in more detail in FIG. 3. They are housed in the beam 20 inside a bore-hole 26, and each consists of a spring 27 and a tappet 28, as represented in FIG. 3.

The spring 27 is placed between the tappet 28 and a plate 29, said plate 29 being fastened to the beam 20 in order to close off the bore-hole 26.

The tappet 28 is axisymmetric in shape with a central base portion 30, said base 30 serving as a supporting surface for the spring 27. Beyond the base 30, on the roller frame 19 side, the tappet 28 comprises a head 31 which presses against said frame 19 and transmits the pressure of the spring 27 to this frame.

The bore-hole 26 comprises, on the roller frame 19 side, a shoulder 32 which retains the tappet 28 by its base.

The plate 29 is fastened to the beam 20 by screws 33 and provides easy access to the spring 27 and to the tappet 28.

FIG. 2 shows the pressure rollers 14 when integrated into a module. In the example represented, this module comprises two independent rollers 14. Each roller 14 is supported by a roller frame 19; these two frames 19 are independent of each other and each comprise their own pressure means 25, and their guide systems 24 cooperate with the reference beam 20.

The beam 20 comprises arrangements 34 at its ends, which make it possible to attach it solidly and in a precise manner to portion 2 b of the general frame 2 of the machine using attachment and alignment screws 35, for example.

Adjustment of the pressure applied by each pressure roller 14 can be done in two ways: replacing the tappet 28 with one having a thicker or thinner base, or changing the spring 27, or changing both the tappet 28 and the spring 27, depending on requirements.

This adjustment can be made directly in the factory, based on the destination of the machine. Such an adjustment, when properly chosen, has the advantage of not permitting improper adjustment changes during normal use, due to the fact that the pressure application elements are inaccessible without appropriate tools. 

1-7. (canceled)
 8. A feeding table comprising, along a path traveled by a plastic film, upstream from a bundling module, pairs of rollers for advancing and maintaining tension on said plastic film and a cutting system for cutting said plastic film, said pairs of roller being supported by a table frame and being arranged respectively upstream and downstream of said cutting system; wherein one of said pairs of rollers is a tensioning pair, arranged downstream from said cutting system, and which comprises a pressure roller which is motorized and, associated with said motorized pressure roller, at least two driven pressure rollers, said driven pressure rollers being arranged so as to form at least two pressure tracks pressing on said plastic film which is traveling between said motorized pressure roller and said driven pressure rollers, and wherein each driven pressure roller is made of steel with an axle supported by a roller frame, said driven pressure rollers being assembled independently of each other, each roller frame being mobile, guided on a beam which acts as a reference and which is solidly attached to said table frame , each roller frame being independent of the other.
 9. The feeding table according to claim 8, comprising a foolproof pressure application system placed between said beam and each roller frame in order to restrain each of said driven pressure rollers and hold said driven pressure rollers in tangential contact with said motorized pressure roller.
 10. The feeding table according to claim 9, wherein said pressure application system comprises at least one coil spring arranged on said beam, said at least one coil spring being associated with a tappet which is guided relative to said beam, said tappet being in contact with and pressing continuously against said roller frame of the corresponding driven pressure roller, due to a force exerted by said at least one coil spring, the number of tappets and coil springs being chosen to establish a given pressure at said tensioning pair, comprising at least three pressure rollers.
 11. The feeding table according to claim 10, wherein said pressure application system comprises at least one pressure element, each pressure element comprising a spring and a tappet and being arranged in a bore-hole created within the thickness of said beam, said bore-hole comprising, at an end on a roller frame side, a shoulder which serves as a support for a base of said tappet, and at another opposed end, a plate acting to cover said bore-hole and serving to support said spring, said plate being removable to allow accessing said pressure element, in order to be able to modify the amount of pressure between the pressure rollers.
 12. The feeding table according to claim 8, wherein said beam has two ends and comprises, at said ends, attachment means for fastening said beam to said table frame.
 13. The feeding table according to claim 12, wherein said attachment means fasten said ends of said beam to a part of said table frame which is retractable to provide access to said pairs of rollers and to said cutting system.
 14. The feeding table according to claim 12, wherein an assembly comprising said driven pressure rollers, said roller frames, and said beam is in the form of a module, said module being equipped with removable attachment means to enable practical and convenient attachment of said assembly onto said table frame. 